Carbon dioxide (CO₂)is readily soluble in water, according to the equation CO₂ + H₂O ↔ H₂CO₃. Carbonic acid (H₂CO₃)is a weak acid. If CO₂ is bubbled into a beaker containing pure, freshly distilled water, which of the following graphs correctly describes the results?

Question

Quizplus · Accepted Answer

When CO2 dissolves in water, carbonic acid is formed. Carbonic acid is a weak acid and will partially dissociate into H+ and HCO3- ions. The increased concentration of H+ ions will cause the pH of the solution to decrease.

Graph B correctly shows that the pH of the water decreases as the concentration of dissolved CO2 increases. The initial pH of the distilled water will be around 7, but as CO2 is bubbled in, the pH will decrease to around 5.5-6 due to the formation of carbonic acid. The other graphs are incorrect because they do not show a decrease in pH.

Carbon Dioxide (CO₂)is Readily Soluble in Water, According to the Equation